There is a need for simple processes to improve the performance of electromaterials such as for batteries or capacitors and supercapacitors, as well as other energy storage and conversion systems. One such example is silicon based anodes in lithium-ion batteries which are regarded as a very promising technology due to having a higher theoretical energy storage densities (3,400-4,200 mAh/g) when compared to conventional graphite lithium cells (350-370 mAh/g).
The capacity of a lithium-ion battery is determined by how many lithium ions can be stored in the cathode and anode. Using silicon in the anode, with carbon particles to assist in conductivity, the battery's capacity increases dramatically because one silicon atom can bond up to 3.75 lithium ions, whereas with a graphite anode six carbon atoms are needed for every lithium atom.
Unfortunately the consequence of this increase in capacity is that during the charge/discharge cycle the silicon in the anode swells and shrinks by up to 400%. Repeated expansion and contraction of this order upon charge/discharge leads to destabilisation of the structure. This leads to reduced capacity and a shorter battery life as the silicon electrode loses stability in a short number of recharge cycles and physically deteriorates. The challenges of maintaining dimensional stability on lithiation exist for all types of silicon materials including its various oxides, composites and alloys. Other examples of electrode active materials having similar expansion/contraction characteristics on charge/discharge include tin- and germanium-based anode materials as well as sulphur-based cathode materials.
Maintaining structural integrity of anode active materials during charge/discharge isn't the only limitation encountered with electrode materials. New cathode active materials having higher energy densities also have resulting integrity problems. Manganese and/or nickel dissolution occurs in cathodes based on lithium manganese nickel oxide materials. Apart from structural loss, such dissolution by the electrolyte can lead to formation of thick Solid Electrolyte Interphase (SEI) layers and consumption of electrolyte. Both of these issues limit battery performance and cycle life.
The present invention addresses at least some of the aforementioned shortcomings of the prior art.
Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.